Efficient recABC-dependent, homologous recombination between coliphage lambda and plasmids requires a phage ninR region gene

A phage lambda gene that gives a 100-fold increase in recombinant frequencies for RecABC pathway-mediated, phage-plasmid homologous recombination (Shen and Huang 1986) maps to ninG (orf-204) of lambda. We call this gene rap, for recombination adept with plasmid. A similar determinant exists in Charon 4A and maps in φ{symbol}80-derived sequences, between nin5 and the Rz homology with lambda. The absence of the Rap⁺ phenotype from certain lambda vectors explains the inefficiency of screening the resulting phage libraries using phage-plasmid homologous recombination. The mapping of rap permits the construction of lambda vectors more suitable for this screening technique.